Featuring a heavyweight trilogy fight between current champ Cain Velasquez and former titleholder Junior dos Santos, UFC 166 takes place Oct. 19 at Houston’s Toyota Center. The evening’s main card airs on pay-per-view following prelims on FOX Sports 1 and Facebook.

Both fights are likely main-card candidates, but UFC officials have yet to reveal their position on the lineup.

Melendez returns to the octagon after suffering a split-decision loss to Benson Henderson in a failed bid for the UFC lightweight title. The 11-year veteran has long been considered one of the best 155-pounders in the world, and the narrow loss was his first defeat in almost five years.

Meanwhile, Sanchez looks to build on the strength of a split-decision win over MMA legend Takanori Gomi at March’s UFC on FUEL TV 8 event in Japan. For that fight, Sanchez dropped to lightweight after a four-fight run at 170 pounds, but he failed to make weight after registering 158 pounds. Still, the win pushed him to 3-1 in his past four fights.

Since his reign in Bellator as the organization’s middleweight champion, Lombard has experienced mixed results in the UFC. The Cuban-Australian and Olympic judoko is just 1-2 in the octagon with split-decision losses to Tim Boetsch and Yushin Okami, and a first-round knockout of Rousimar Palhares. Prior to joining the UFC, the 35-year-old has posted a 25-fight unbeaten streak. Lombard, who’s ranked No. 12 in the USA TODAY Sports/MMAjunkie.com MMA middleweight rankings, now heads to welterweight.

He meets Marquardt, a former Strikeforce champion who returned to the UFC in March. However, Marquardt, who also unsuccessfully vied for the UFC middleweight title in 2007, suffered a knockout loss to Jake Ellenberger at UFC 158. It marked the first back-to-back losses of his career, which included a Strikeforce title loss to Tarec Saffiedine in January.